linux-kernel - Re: [PATCH rdma-next v1 1/2] lib/scatterlist: Fix wrong update of orig

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Date:   Wed, 30 Jun 2021 14:16:56 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Maor Gottlieb <maorg@...dia.com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Zhu Yanjun <zyjzyj2000@...il.com>,
        Christoph Hellwig <hch@....de>,
        Robin Murphy <robin.murphy@....com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH rdma-next v1 1/2] lib/scatterlist: Fix wrong update of
 orig_nents

On Wed, Jun 30, 2021 at 01:12:26PM +0200, Marek Szyprowski wrote:
> Hi Leon,
> 
> On 29.06.2021 10:40, Leon Romanovsky wrote:
> > From: Maor Gottlieb <maorg@...dia.com>
> >
> > orig_nents should represent the number of entries with pages,
> > but __sg_alloc_table_from_pages sets orig_nents as the number of
> > total entries in the table. This is wrong when the API is used for
> > dynamic allocation where not all the table entries are mapped with
> > pages. It wasn't observed until now, since RDMA umem who uses this
> > API in the dynamic form doesn't use orig_nents implicit or explicit
> > by the scatterlist APIs.
> >
> > Fix it by:
> > 1. Set orig_nents as number of entries with pages also in
> >     __sg_alloc_table_from_pages.
> > 2. Add a new field total_nents to reflect the total number of entries
> >     in the table. This is required for the release flow (sg_free_table).
> >     This filed should be used internally only by scatterlist.
> >
> > Fixes: 07da1223ec93 ("lib/scatterlist: Add support in dynamic allocation of SG table from pages")
> > Signed-off-by: Maor Gottlieb <maorg@...dia.com>
> > Signed-off-by: Leon Romanovsky <leonro@...dia.com>

<...>

> For now I would suggest to revert this change.

Thanks for the report, we will drop this patch.